Abstract:

The mechanism of high-Tc superconductivity remains a challenging problem in condensed matter physics. Some of the fundamental issues, such as the pairing symmetry, remain unsettled. In this talk, we report our recent endeavors by using ultrathin Bi2Sr2CaCu2O8+δ (BSCCO) superconductors. To study the pairing symmetry, we fabricate ultrathin twisted high-Tc Josephson junctions with atomically flat interfaces. We demonstrate that the Josephson current solely arises from the coupling between the rotated double copper-oxide planes. Notably, the Josephson coupling strength reached the same level for different twist angles, indicative of an s-wave pairing [1] than the widely expected d-wave pairing. We further study the magneto-transport properties of BSCCO flakes across a wide doping regime. In the lightly doped regime, we observe Little-Parks like resistance oscillations [2]. This result is surprising as it indicates that a spatially periodic order emerges spontaneously in the system.

[1] Y. Zhu et al., Phys. Rev. X 11, 031011 (2021).

[2] M. Liao et al., Nat. Commun. accepted (2022).